The Royal Canadian Henley Regatta
The nearby waterway, a part of the first Welland Canal constructed in 1824-29, is the course used for the annual Royal Canadian Henley Regatta. Competitive rowing became popular in Canada during the 1860's and 1870's, and in 1880 the Canadian Association of Amateur Oarsmen was formed in Toronto. This body held an annual regatta for international oarsmen in various Canadian centres until, in 1903, Port Dalhousie was selected as the permanent site. This rowing event, inspired by the famous regatta held yearly at Henley-on-Thames in England, has become one of the largest in the world.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.